It is known in the prior art the construction of containers in metal sheet, such as cans and pails, in which the side wall presents a square, rectangular or cylindrical contour, and the upper wall is provided in a single piece or in the form of a substantially circular large opening defined internally to a closure seat formed on the upper wall, throughout the opening periphery and incorporating a pending peripheral wall in whose interior the press-fit lid is seated.
In certain constructions, the pending peripheral wall, whose upper edge defines the closure seat, operates only as a sealing and retention element, by simple friction, in relation to a side wall of the press-fit lid to be fitted in the interior of said pending peripheral wall of the annular upper wall of the container.
In an also known construction object of the Brazilian Patent PI 9408643-5 of the same applicant, the lower portion of the pending peripheral wall is bent to the interior of the opening of the container, upwardly, until its free end edge reaches a position adjacent to said pending peripheral wall. In this previous construction of the same applicant, the pending peripheral wall, which surrounds and defines the discharge opening, incorporates a continuous tubular rib of circular cross-section, disposed in a plane lowered in relation to the plane of the closure seat, that is, of the upper edge of the pending peripheral wall.
Also according to the already filed prior solution, it is provided a lid presenting a peripheral edge, generally defined by an outwardly and downwardly bent continuous bead, from which downwardly projects a circular side wall provided with a peripheral recess, with an approximately semi-circular section and dimensioned to be fitted around the continuous tubular rib upon seating the lid on the discharge opening of the container. The peripheral edge is seated onto the closure seat when the lid is fitted on the discharge opening.
Although resulting in an excellent axial locking of the lid in the closed condition, and also eliminating the risks of manual handling injuries and of contamination of the stored product by contacting non-varnished parts of the metal sheet of the container, said prior art solution object of the Brazilian Patent PI 9408643-5 still needs to present an increased structural strength to comply with the specifications required for the containers containing dangerous products.
As known, the containers in metal sheet for storing dangerous products must withstand a determined level of inner pressure during a certain period of time, without the can being subjected to a structural deformation which impairs the tightness of the container and the seating of the press-fit lid on the closure seat. In this respect, the constructive solution object of the Brazilian Patent PI 9408643-5, optionally associated with the construction proposed for the annular upper wall object of the Brazilian Patent PI 0006493-9, also of the present applicant, allows maintaining the integrity of the container when it is submitted to the limit pressure conditions required for certifying the package as appropriate for containing dangerous products.
However, although said prior solutions guarantee an adequate retention of the lid on the closure seat in the pressure test conditions for dangerous products, they do not guarantee the integrity of the closure when the container, filled with the product, is submitted to a free fall, from a test height of usually 0.80 m to 1.5 m and against a rigid surface, with the lid turned downwards at an angle inclined at about 45°.
In the type of fall cited above, the upper marginal region of the container, to which is double seamed the annular upper wall, is submitted to a deformation or “inward denting”, which can deform the closure seat at a degree sufficient to destroy the tightness of the container, even if this deformation is still insufficient to produce ejection of the lid.
Said destructive deformation of the closure seat mostly results from the higher resistance to deformation by axial forces and from the lower resistance to deformation by radial forces to which the region of the side wall of the container, which is adjacent to the impact region, is submitted during the free fall test in the inclined position.
Depending on the characteristics of the sheet used for manufacturing the container, it is also possible to have a deformation of the double-seam in the impact region, sufficient to impair the perfect tightness of the container provided with an annular upper wall (as discussed above), or with a single-piece upper wall. The problem regarding loss of tightness, caused by excessive deformation of the double-seam in the impact region, can occur both in the double-seam of the upper wall, when the container is allowed to fall in the inverted position, and in the double-seam of the lower wall, when the container is allowed to fall in the inclined but not inverted position. The deficiencies commented above can be particularly associated with the 18 liter square cans largely used in the market and in which the upper wall is provided in a single piece which is peripherally double seamed, or as an annular upper wall carrying the closure lid.
It was also verified that the containers with a cylindrical or polygonal cross-section, generally square or rectangular, presenting a storage capacity of 1 gallon and of 9 and 5 liters, respectively, and having an upper wall in a single piece and optionally provided with a respective lid, are also vulnerable to the occurrence of loss of tightness by excessive deformation of the double-seam when submitted to impact caused by the container falling in an inclined position.
In the containers with a polygonal cross-section, the double-seam regions more vulnerable to the loss of tightness are those which define the rounded vertices of the polygonal transversal contour of the upper and lower walls, which vertices define the upper and lower ends of the respective rounded longitudinal edges of the container.
When a container of polygonal cross-section of the type considered herein is dropped in the inclined position, inverted or not, so that a vertex of one of the upper or lower walls touches the impact surface, the double-seam region, which defines this vertex, may be submitted to an excessive deformation sufficient to destroy the tightness of the container in said deformed double-seam region. Although the problem regarding loss of tightness is more common in the region of the vertices when these define the impact region when the container falls, it can also occur in other rectilinear or bent double-seam parts, as in the case of the cylindrical containers.
In the containers in which the accentuated deformation of the peripheral end edges, defined by the double-seams, has no actual influence on the integrity of the lid seat and on the retention and tightness of said lid, it is very important to maintain the perfect tightness in the double-seam regions, particularly in metal sheet containers used for containing products considered hazardous.
Some of the known solutions, in order to minimize the problem related to the deformation of the closure seat and of the double-seam regions, when submitted to impact caused by the free fall of the fully loaded container and during test conditions, require the provision of auxiliary protecting devices aggregated to the container and which considerably raise the packaging cost.
Another known solution, in order to eliminate or minimize the problem regarding deformation of the closure seat and double-seam regions, upon fall of the container, is defined in documents BR 0201566-8 and DT 24 17 517 A1.
In this type of prior art solution, the tubular side wall of the container body is provided, in its upper and lower regions, adjacent to the upper and lower double seamed edges of the container, with a plurality of circumferential grooves in the form of an open V, with its opposite sides being symmetrical in relation to a median plane orthogonal to the axis of the container. Although constituting zones to be plastically deformable when the container falls in an inclined position, with the purpose of absorbing the impact energy and avoiding losing the tightness of the closure seat of the lid, if existing, and of the double-seam region submitted to deformation, this type of circumferential groove with the cross section in the form of a symmetrical V presents reduced capacity for absorbing deformation energy, requiring a higher number of grooves to absorb the deformation of the side wall and to avoid damages to the tightness of the container, but which impairs the capacity of the container to resist the stacking forces required by the current specifications.
Besides, the symmetrical V shape of the known grooves makes the tubular side wall of the container fragile to resist the compression forces, which impedes reducing the thickness of the metal sheet constitutive of the container body. Thus, the metal sheet has to be maintained with a thickness which guarantees the structural strength of the containers when submitted to compression forces upon stacking.
The rounded V-shaped grooves with a large opening angle and a reduced radial depth, as it occurs in the solution DT 24 17 517 A1, allows a high stacking structural strength to be obtained. However, this rounded V-shape with a large opening angle impairs the plastic deformation of the groove sides to absorb the impact energy.